class Solution {
public:
    int peakIndexInMountainArray(vector<int>& arr) {
        int left=0,right=arr.size()-1;
        while(left<right)
        {
            int mid=left+(right-left)/2;
            if(arr[mid]<arr[mid+1]) left=mid+1;
            else if(arr[mid]>arr[mid+1]) right=mid;
        }
        return left;
    }
};
